WAD  , a

black, earthy mineral consisting mainly of hydrated manganese dioxide; of importance as an ore . Being an amorphous substance, it varies considerably in chemical composition, and contains different impurities often in large amount . A variety containing much cobalt oxide is called " asbolite," while " lampadite " is a cupriferous variety . It is very soft, readily soiling the fingers, and may be considered as an earthy form of psilomelane (q.v.) . It results from the decomposition of other manganese minerals, and is often deposited in marshes (" bog manganese ") or by springs . The name wad is of uncertain origin, and has been applied also to graphite . (L . J .